There are known in the art apparatuses, for example gauges of the so-called “plug” type, for checking the diameter of holes, for example before or after the machining in machine tools like grinding machines.
U.S. Pat. No. 4,348,814 discloses examples of such gauges, in which a measuring armset coupled to a support includes two feelers fixed to movable arms in diametral opposite positions, for contacting the surface of the hole to be checked. A transducer detects reciprocal displacements between the movable arms and provides electric signals indicative of the mutual position of the feelers.
U.S. Pat. No. 4,339,879 discloses a multiple plug gauge for checking a hole with cross-sections with different nominal diameter, including pairs of cells with one feeler each, coupled to a central support, at diametrically opposite positions, at portions of suitable diameter that form the support. The cells are coupled in a limitedly adjustable way, thanks to the coupling of fastening screws in shaped holes, so that the position of the measuring heads along a direction parallel to the axis of the plug gauge and along transversal directions can be adjusted about a reference position.
The structure of the multiple gauge described in the herein secondly mentioned U.S. patent is aimed at checking holes with well defined characteristics, matched by the shape and dimensions of the central support. Thus, although the position of the single cells on associated, dedicated portions of the support is limitedly adjustable, the overall structure of the gauge does not enable a flexible use for checking holes with different configurations. Furthermore, the structure and the utilized components limit the possibility of simultaneously performing the checking of diameters at nearby cross-sections along the longitudinal axis of the hole, a checking that is frequently requested, and generally carried out in ways that are not entirely satisfactory in terms of costs, time and convenience.